US President Barack Obama is predicting the alleged September 11 mastermind will be convicted and sentenced to death.

From the president down, the Obama administration has come out swinging to defend the decision to put Khalid Sheikh Mohammed on trial in New York.

Meanwhile, Mr Obama has acknowledged for the first time that he will not meet his January deadline to shut Guantanamo Bay.

He says the United States has nothing to fear from putting Khalid Sheikh Mohammed on trial.

"I don't think it will be offensive at all when he is convicted and when the death penalty is applied to him," Mr Obama said.

The president says he has complete confidence in the tough prosecutors from New York who specialise in terrorism and he insists he is not prejudging the outcome.

"I think this notion that somehow we have to be fearful, that these terrorists possess some special powers that prevent us from presenting evidence against them, locking them up and exacting swift justice, I think that has been a fundamental mistake," he said.

The five men face trial in a courtroom just blocks from where the World Trade Centre stood.

US attorney-general Eric Holder says he knew the decision would be controversial but has declared he is not scared of what is to come.

"And if Khalid Sheikh Mohammed makes the same statements he made in his military commission proceedings, I have every confidence that the nation and the world will see him for the coward that he is," Mr Holder said.

"I'm not scared of what Khalid Sheikh Mohammed has to say at trial and no-one else needs to be afraid either."

But Republican Senator Jon Kyl has challenged him to say how a civilian trial would be better than a military commission.

"How could you be more likely to get a conviction in federal court, when Khalid Sheikh Mohammed has already asked to plead guilty before military commission and be executed?" he said.

Mr Holder says the nation's intelligence secrets will be protected during a public trial in a civilian court and he denies the trial will give Khalid Sheikh Mohammed a world stage to spout hateful rhetoric.

"We need not cower in the face of this enemy," Mr Holder said.

"Our institutions are strong, our infrastructure is sturdy, our resolve is firm and our people are ready."

But the Obama administration is not ready to shut down Guantanamo Bay by the president's January deadline.

"Guantanamo, we had a specific deadline that was missed," Mr Obama said.

The president says he is not disappointed the deadline has slipped, adding that he knew it was going to be hard.

He says he still hopes to close Guantanamo Bay next year, although he has not set a new deadline.